1. Field of the Invention
Embodiments of the present invention relate generally to a system method for using a directed beam of energy to selectively sinter metal powder to produce or repair a part; and specifically, to the use of selective laser sintering (SLS) and scanning laser epitaxy (SLE) to produce or repair a full density metal part.
2. Background of Related Art
Since its inception in the 1930's, the gas turbine engine has grown to be the workhorse power plant of modern aircraft. Over the years, there have been significant advances in the technology related to aircraft propulsion systems and the methods of manufacturing these system components. Associated with the technological advances has been a desire to reduce engine life cycle costs by minimizing acquisition, operating, and maintenance costs. While there are many ways to reduce engine life cycle costs, one approach may be through technological developments such as advanced materials, innovative structural designs, improved aerothermodynamics, improved computational methods, and advanced manufacturing techniques.
Traditional manufacturing techniques have typically coupled the cost of manufacturing a part with the volume of parts produced. Manufacturing techniques that are designed for large scale production, such as casting and extrusion are often cost effective, but these manufacturing techniques are generally unacceptable for small quantities of parts. Another traditional manufacturing technique for producing parts is powder metallurgy which requires a tool for shaping the powder, therefore often rendering the powder metallurgy process unattractive for producing a limited quantity of parts.
Where only a small quantity of parts is desired, conventional subtractive machining methods (e.g., CNC milling machines) are often employed to produce the part. A conventional subtractive machining method utilizes the removal of a portion of the material from the initial block of material to produce the desired shape. Examples of conventional subtractive machining methods include: broaching, drilling, electric discharge machining, flame cutting, grinding, turning, etc. While the conventional subtractive machining methods are usually effective in producing the desired component, they have a multitude of limitations.
There are other manufacturing processes which are additive in nature. The type of processes that would be classified as additive in nature include plating, cladding, flame spraying, welding, laminating, etc. However, these processes are generally used in conjunction with the conventional subtractive machining techniques to produce a component that cannot be directly machined.
Solid Freeform Fabrication (SFF) is a group of emerging technologies that have revolutionized product development and manufacturing. The common feature shared by these technologies is the ability to produce freeform, complex geometry components directly from a computer generated model. SFF processes rely on the concept of layerwise material addition in selected regions. A computer generated model serves as the basis for making a replica. The model is mathematically sliced and then each slice is recreated in the material of choice to build a complete object.
An early application of SFF technologies was in the area of Rapid Prototyping (RP). RP enables engineers to quickly fabricate prototypes in a fraction of the time, and at typically less than half the cost, when compared with conventional prototyping methods. The tremendous economy of RP is facilitated by its high degree of automation, both in the design, using computer aided design (CAD), and fabrication cycles. On the manufacturing side, computer driven RP machines can accept CAD solid models as input to automatically create a physical realization of the desired component. The overall advantage of this powerful combination is the ability to rapidly iterate through several design and prototyping cycles before “freezing” the design for final production at significantly lowered costs and shorter “time to market.”
Most RP technologies were initially developed for polymeric materials. These technologies allowed designers to rapidly create solid representations of their designs in a surrogate material for design visualization and verification. Further demand for functional prototypes led to the development of materials and processes that enabled production of prototype patterns and parts that could be subjected to limited testing for form and fit. Major developments have taken place next in the area of SFF known as Rapid Tooling. The focus of this area has been to develop SFF technologies to enable rapid production of prototype tooling for a variety of manufacturing techniques including injection molding, electro-discharge machining and die casting. The growth in this area has been spurred by the economical advantages of making limited run prototype tooling via SFF as compared to conventional techniques.
Over the past ten years, there has been an explosion in the development and growth of SFF technologies. These technologies can be broadly categorized into three classes, namely transfer, indirect, and direct SFF methods. Transfer methods are those methods that use a pattern or sacrificial intermediary to generate the desired component whereas “indirect” methods are those SFF methods that directly produce intermediate density parts that undergo post-processing such as conventional sintering and infiltration to attain full density. Direct methods are methods that directly produce fully dense or near fully dense complex shaped parts in the desired composition (e.g. metal, ceramic or cermet) by applying a geometry and property transformation to the material with minimal post-processing requirements. In the context of making metal components by SFF, a number of “transfer” and “indirect” methods are available.
What is needed, however, is a direct SFF technique capable of creating functional, fully dense, metal and cermet components via the direct, layerwise consolidation of constituent powders. The system should eliminate of expensive and time-consuming pre-processing and post-processing steps. The system and method should be suitable for use with nickel and cobalt base superalloys, superalloy cermets, titanium base alloys and monolithic high temperature metals such as molybdenum. It is to such a system and method that embodiments of the present invention are primarily directed.